In the field of digital watches, a certain number of solutions which make it possible to establish an electrical connection between the watch and an external device are already known. Documents U.S. Pat. No. 4,118,922, U.S. Pat. No. 4,323,996, U.S. Pat. No. 4,103,483 and U.S. Pat. No. 4,165,605 describe for example a certain number of solutions which consist in placing one or more electrical contact elements in the bottom of the casing of the watch, in an area where the watch is in contact with the user's skin, the electrical connection with these contact elements being guaranteed by an adaptor or by suitable contact means.
The proximity of the electrical contact elements of the watch to the user's skin is an important constraint. It is indeed desirable, as a general rule, to avoid all contact of these elements with the user's skin. Mechanical or electrical means of protection must typically be provided in order to limit this risk. On the other hand, these solutions are subject to dirtying or contamination problems which impair the quality of the electrical connection.
More desirable solutions for tackling the problem of a possible contact with the user's skin have already been suggested. The document U.S. Pat. No. 5,703,460 describes for example an electrical connection device using a plug-in adaptor which is inserted into a socket provided laterally in the watch casing. Although it allows all contact with the user's skin to be avoided, this solution nonetheless has the disadvantage of only allowing the establishment of an electrical connection with a single contact element (an additional plug-in adaptor being necessary for the establishment of an electrical connection with a supplementary contact element in the watch) and of being more severely subject to contamination problems, dirt and impurities accumulating in the bottom of the socket as the watch is used. Moreover, the configuration of the connection device is not suitable from the viewpoint of guaranteeing the water resistance of the portable instrument.
Another solution using a plug-in adaptor is illustrated by the document JP 2001-186584. This document describes a portable electronic instrument taking the form of a wrist-watch provided with a connection device ensuring an electrical link with a pair of headphones. The plugging-in of the pair of headphones is ensured by a conventional jack-type adaptor. In the context of this application, the adaptor has three electrical contact zones aligned the one behind the other in the direction of insertion of the adaptor into its socket. In the same way, this socket is provided with three electrical contact elements also aligned the one behind the other in the direction of insertion of the adaptor, these three contact elements being electrically linked to the electrical and electronic components housed in the casing of the instrument. It should be noted that the socket Into which the adaptor is to be plugged in is not as such arranged directly in the casing of the Instrument, but into an additional casing attached to the casing of the Instrument, the electrical connection between the two casings being ensured by components of a similar construction to that of a push-button.
This solution has the advantage of requiring only a single plug-in connector to establish a plurality of electrical connections, as well as constituting a relatively widespread standard on the market This solution Is however always Ill-adapted with regard to the sealing constraints of the portable Instrument and is also very sensitive to the build-up of dirt or impurities which may Impair the quality of the electrical contact. Moreover, the construction of such a device remains relatively complex and is not very robust in use.